text: #ifndef JOS_KERN_MONITOR_H
  #define JOS_KERN_MONITOR_H
  #ifndef JOS_KERNEL
  # error "This is a JOS kernel header; user programs should not #include it"
  #endif
  
  struct Trapframe;
  
  // Activate the kernel monitor,
  // optionally providing a trap frame indicating the current state
  // (NULL if none).
  void monitor(struct Trapframe *tf);
  
  // Functions implementing monitor commands.
  int mon_help(int argc, char **argv, struct Trapframe *tf);
  int mon_kerninfo(int argc, char **argv, struct Trapframe *tf);
  int mon_backtrace(int argc, char **argv, struct Trapframe *tf);
  int mon_showmappings(int argc, char **argv, struct Trapframe *tf);
  
  #endif	// !JOS_KERN_MONITOR_H
  